1. Field of the Invention
The present invention relates to methods of making molds in which articles having an optical surface, such as contact lenses, are formed.
2. Description of the Related Art
Various methods which are known for the production of molded articles having an optical surface, such as contact lenses, involve forming the articles in reproducible plastic molds.
U.S. Pat. Nos. 4,121,896 and 4,208,364 (Shepherd) disclose a static cast molding method for the production of contact lenses. The molds, in which the contact lenses are cast, comprise a thermoplastic male mold portion having a first molding surface to form one of the contact lens surfaces, and a thermoplastic female mold portion having a second molding surface to form the other contact lens surface. A plurality of each of the thermoplastic male and female mold portions are produced from a set of metal master molds which are fabricated by traditional machining and polishing operations.
U.S. Pat. No. 4,681,295 (Haardt et al.) discloses a tricurve optical metal master mold. The tricurve metal master mold, in conjunction with a base curve metal master, are used to prepare thermoplastic replica molds by conventional injection molding techniques, with reference to the above-identified Shepherd patents. The thermoplastic replica molds are used to static cast contact lenses having the desired tricurve configuration at the convex lens surface and the desired base curve at the concave lens surface. According to the disclosure, machining of the tricurve metal master is an exacting, complicated, precise and permanent operation, and subsequent polishing of the tricurve metal mold blank is also an operation that requires care and precision.
U.S. Pat. No. 4,865,779 (Ihn et al.) discloses a mold for the manufacture of lenses which has an anterior molding part and a posterior molding part each of which has a molding surface for forming one of the optical surfaces of the lens. The tools used to make the molds generally comprise an anterior tool and a posterior tool, each comprising an optical insert. The reference discloses that known machining and polishing operations may be used to manufacture the tools, and the tools may be fabricated from various metals.
U.S. Pat. No. 4,605,524 (Danker) discloses a method of casting a bifocal contact lens. Metallic master dies are machined to the curved surfaces necessary for the lens, and plastic casting dies, in which the contact lens is cast, are made from these metallic master dies. The master die for the anterior surface of the lens has an insert or plug of steel. The reference discloses that precision machining is generally necessary for the surfaces of the carrier and the plug which fit together, as well as for the curved surfaces corresponding to the prescription for near vision.
U.S. Pat. Nos. 4,179,484, 4,188,353 and 4,307,046 (Neefe) disclose methods of making lenses employing a single mold having an optical surface. In the '484 patent, a lens mold made of a resinous material is formed from a master mold, so as to form a resinous mold having a cup-like cavity with a curved convex surface. Subsequently, the mold is processed so as to distort the curved surface to a toric shape. A liquid monomer material is cast in the mold to produce an article having a toric concave lens surface. The convex lens surface is then cut from the hardened lens material.
In the '046 patent, a lens mold made of a resinous material is formed from a master mold, similar to the '484 patent, to form a resinous mold having a cup-like cavity with a curved convex surface, and a liquid monomer material is cast in the mold to produce an article having a concave lens surface. The convex lens surface is then cut from the hardened lens material, and the patent discloses that a carbon dioxide laser may be used to cut this optical surface.
In the '353 patent, a lens mold made of a resinous material is formed from a master mold, similar to the '484 patent, to from a resinous mold having a cup-like cavity with a curved convex surface. Subsequently, the mold is processed so as to distort the curved surface to an aspheric shape, and a liquid monomer material is cast in the mold to produce an article having an aspheric concave lens surface. The convex lens surface is then cut from the hardened lens material.
In each of the above Neefe patents, the master mold is disclosed as made from glass or stainless steel or other materials which will withstand the molding temperatures. In the '484 and '046 patents, which disclose the material used for the master mold in the working embodiments, the master mold is disclosed as being made from steel.
U.S. Pat. No. 5,110,278 (Tait et al.) discloses an injection molding apparatus for producing a toric lens casting mold arbor. The mold arbor includes a hollow, cup-like top portion having a toric surface. Lens buttons having a precision toric base curve and a generally flat front surface are molded in the cup-like top portion of the mold arbor. The toric surface of the cup-like top portion is formed upon injection molding from a toric core pin which has a concave toric end surface. The patent discloses that the toric core pin is made of metal, such a stainless steel, nickel or nickel alloy, or any other suitable permanent material, and the toric surface on the toric core pin may be produced by known manufacturing procedures, including lathe machining followed by polishing, electroforming, or electro discharge machining followed by polishing. Subsequent to molding the button with the toric lens surface, the other lens surface is lathe cut from the generally flat front surface.
According to the conventional methods for the production of plastic molds, the plastic molds are formed from a metal master mold by known injection or compression molding techniques, wherein the molding surfaces of the plastic molds are formed from a metal tool. For the production of articles having an optical surface, such as contact lenses, the metal tool is provided with an optically smooth molding surface. The machining and polishing operations for providing an optically smooth surface on the metal tools can be exacting, complicated and time-intensive, especially for irregularly shaped molding surfaces, such as a molding surface corresponding to a toric contact lens surface. Further, operator errors during the machining or polishing operation may require starting anew the machining operation or even scrapping the metal tool altogether.